Camshaft and method for manufacturing a camshaft

ABSTRACT

A camshaft and a method for manufacturing the camshaft as described. A gear wheel of the camshaft is mounted on a camshaft tube. A collar that is attached to the gear wheel and a locating bearing element that is mounted on the camshaft tube delimit a locating bearing seat of the camshaft.

CROSS REFERENCE TO RELATED APPLICATIONS

This present application is a national stage of PCT International Application No. PCT/EP2006/006861 filed Jul. 14, 2006 which claims priority under 35 U.S.C. § 119 to German Patent Application No. 10 2005 034 777.0 filed Jul. 26, 2005, the entire disclosures of which are expressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a camshaft and to a method for manufacturing a camshaft.

Shaping and axially securing a camshaft locating bearing to an adjacent camshaft wheel or gear wheel are currently performed on assembled camshafts by a flange which is incorporated into the camshaft by welding or press-fitting. In such case, the camshaft is typically in the form of a steel cylinder of solid material. The use of a press-fit or welded flange necessitates a further work step, however, making manufacture more expensive. In particular, the camshaft must be re-clamped, which can result in errors in re-clamping.

DE 37 04 092 C1 describes a hollow shaft and a method for manufacturing it. This hollow shaft comprises a base body that has varying internal and external radii in the axial direction, while the wall thickness remains the same. It is provided for connecting torque-transmitting structural elements such as gear wheels, cams and the like to the base body, in particular in regions of relatively large internal and external radii.

DE 195 02 834 A1 discloses an arrangement for mounting a component. This arrangement includes, among other things, a camshaft that has a cylindrical inner wall and an outer wall that has an external diameter that varies both radially and axially. In a region in which the camshaft has a particularly large external diameter, a cam is integrated into this camshaft as part of the outer wall. A cam wheel that forms an additional element in a region of the outer wall of the camshaft is secured thereto.

Taking this as a starting point, an object of the present invention is to provide a camshaft of low mass and high stability that is simple and inexpensive to manufacture.

For this purpose, a camshaft having the features described below and a method for manufacturing such a camshaft, as also described below are provided.

In the case of the camshaft according to the invention, a gear wheel is mounted on a camshaft tube. A collar that is attached to the gear wheel and a locating bearing element that is mounted on the camshaft tube delimit a locating bearing seat of the camshaft.

In contrast to prior assembled camshafts in which a separate, friction-welded collar or journal creates a weakening such that a predetermined break point is created, the so-called assembled camshaft according to the present invention is made uniform without a weakening of the material.

The gear wheel having the collar, like all the other components of the camshaft—that is to say the locating bearing element and the cam, shafts and the like—is seated without any packing for the camshaft tube directly on the camshaft tube. Thereby a secure gear wheel seat is provided, with the camshaft tube being hollow in form, in particular in a region of the gear wheel seat.

The fact that, in the case of the assembled camshaft according to the invention, the gear wheel having the collar, or a camshaft wheel having an attached collar, is seated not on a steel cylinder like other assembled camshafts but on the hollow camshaft tube proves to give a weight advantage over other constructions having steel cylinders of solid material. Apart from extremely low-cost manufacture of this assembled camshaft, the locating bearing seat that is provided for receiving a locating bearing or a camshaft locating bearing is simple to create and can be positioned precisely, along the camshaft. The locating bearing seat is generally formed or delimited by two locating bearing elements that are offset from one another in the axial direction on the camshaft tube.

It is true that, instead of a simple cylindrical camshaft tube as the camshaft body, other known camshafts have hollow bodies, but the bodies of such camshafts (as disclosed, for example, in DE 37 04 092 C1 or DE 195 02 834 A1) have outer and/or inner walls having radially and/or axially varying radii.

Bodies of this known type, which are complex to manufacture, are not required for the camshaft of the present invention. Individual components of the camshaft such as the gear wheel, locating bearing elements, cams, shafts and the like are mounted directly on a cylindrical outer wall or cylindrical casing of the camshaft tube in a simple manner by suitably positioning them axially and radially in relation to one another. Thereby, a respective two of these components are at a suitable spacing from one another and in a suitable alignment in relation to one another once they have been secured to the camshaft tube. This locating bearing seat, which is delimited by the locating bearing element and the collar of the gear wheel, is provided, for example, for receiving a locating bearing or locating bearing ring on the camshaft tube and thus the camshaft.

In particular, the collar may be at the side of the gear wheel. This collar, once it is attached to the gear wheel, forms a way of securing the gear wheel axially to the camshaft, and an axial one-sided or, in normal cases, two-sided wearing element for the locating bearing seat.

The gear wheel and the locating bearing element (it being possible for the locating bearing element to be in the form of a wearing disk or, alternatively, a cam or special cam with a preferably integrated ring) are mounted on the camshaft tube by a suitable joining method.

In a preferred embodiment, the gear wheel and/or the locating bearing element are shrunk-fit onto the camshaft tube. For this purpose, the gear wheel having the collar and/or the locating bearing element are heated, and while at a temperature which is higher than that of the camshaft tube they are drawn onto the camshaft tube and put into a suitable axial and radial position. Once the temperature of the gear wheel having the collar and/or the locating bearing element and that of the camshaft tube have equalized, there is a form-fitting shrink-fit connection between the gear wheel having the collar and/or the locating bearing element and the camshaft tube.

In addition, a way of axially and radially securing the locating bearing that is to be arranged in the locating bearing seat is formed by the shrink-fit connection or a shrink-fit seat or, where appropriate, by another suitable way of securing the locating bearing elements. The gear wheel and/or the locating bearing element are secured to the camshaft tube axially and/or radially by the shrink-fit seat or a correspondingly secured locating seat. The camshaft tube gives the camshaft an overall length. The gear wheel may be secured to the end of the camshaft tube.

In the method according to the present invention for manufacturing a camshaft, a locating bearing element and a gear wheel to which a collar is attached are mounted on a camshaft tube such that the locating bearing element and the gear wheel provide a delimitation of a locating bearing seat for the camshaft along the camshaft tube.

When the inventive method is carried out, the gear wheel having the collar and/or the locating bearing element (it being possible for the locating bearing element to be in the form either of a wearing disk or of a cam, for example a special cam, with an integrated ring) are shrunk-fit onto a cylindrical outer wall of the camshaft tube. The collar is attached to the side of the gear wheel before the gear wheel is mounted on the camshaft tube. Thereby this collar forms, together with the locating bearing element (that is the wearing disk or the cam having the ring) the locating bearing seat. A so-called assembled camshaft is manufactured by the present method.

One advantage of the present invention is the low cost of manufacture. Moreover, manufacturing the locating bearing seat for the locating bearing may be carried out more simply and precisely than with other manufacturing methods, since no corrective measures for making a connection between a journal and the camshaft tube are required.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic view showing a first embodiment for shaping a seat for a locating bearing and gear wheel in an assembled camshaft;

FIG. 1 b is a sectional view of the embodiment shown in FIG. 1 a;

FIG. 2 a is a schematic view showing a second embodiment for shaping a seat for a locating bearing and gear wheel in an assembled camshaft;

FIG. 2 b is a sectional view of the embodiment shown in FIG. 2 a;

FIG. 3 a is a schematic view showing an assembled prior art camshaft; and

FIG. 3 b is a sectional view of the assembled prior art camshaft shown in FIG. 3 a.

DETAILED DESCRIPTION OF THE DRAWINGS

The drawing figures are described together and as a whole, and like reference numerals relate to like components in each of the figures.

For the purpose of understanding the invention, FIGS. 3 a and 3 b show how a locating bearing seat 33 and a seat of a gear wheel 35 are shaped on an assembled camshaft 37 in accordance with the prior art. Here, the camshaft 37 and its components are presented in a sectional illustration in FIG. 3 b.

A base body 39 of this camshaft 37 is of solid construction and has along an outer wall different external radii which are cylinder-symmetrical and are manufactured, for example, by casting and/or machining processes such as grinding. The gear wheel 35 of the camshaft 37 is in this case seated on a steel cylinder of solid material. The locating bearing seat 33 is thus delimited by two portions 41, 43 of the base body 39 that have a relatively large external radius. At one end of the camshaft 37, a flange 45 is connected to the base body 39 by welding or contact pressure. The gear wheel 35 is secured to this flange 45.

During manufacture, the base body 39 has additionally to be equipped with a locating bore 47 for an assembly process and a grinding location 49 for a grinding process that is additionally to be carried out. In addition, the camshaft 37 must be re-clamped during manufacture, and this operation can result in errors in re-clamping. A spindle of the prior art camshaft 37 comprises two parts, the base body 39 and the flange 45. As a result, the construction of this camshaft 37 is weakened and to a certain extent has a predetermined break point.

FIGS. 1 a and 1 b each show portions of a first embodiment of a camshaft 1 according to the invention. The camshaft 1 and individual components of the camshaft 1 are presented in a sectional illustration in FIG. 1 b. This so-called assembled camshaft 1 has a camshaft tube 3. This camshaft tube 3 is hollow on the inside and has a cylindrical inner wall and a cylindrical outer wall. The inner wall and the outer wall are coaxial in relation to one another.

The following components are mounted on the camshaft tube 3: a gear wheel 5 that is provided for driving the camshaft 1 is arranged at the end of the camshaft tube 3 and has a laterally attached collar 7; and a locating bearing element in the form of a wearing disk 9.

When the camshaft 1 is manufactured, the gear wheel 5 and the wearing disk 9 are drawn directly onto the cylindrical outer wall of the camshaft tube 3 and are positioned axially and/or radially on the camshaft tube 3 in suitable manner. The gear wheel 5 having the collar 7, and the locating bearing element in the form of a wearing disk 9, are secured by shrink-fitting.

A locating bearing seat 11 is formed and delimited along a portion of the outer wall of the camshaft tube 3, by the locating bearing element or wearing disk 9 and the lateral collar 7 of the gear wheel 5, such that a gear wheel seat is provided. This locating bearing seat 11 is provided for the purpose of receiving a locating bearing or locating bearing ring (not illustrated). The camshaft tube 3 has, at least in the region of the locating bearing seat 11 and the gear wheel seat (i.e., in the region that is illustrated in FIGS. 1 a and 1 b) a constant wall thickness.

The camshaft 1 has a further component that is only illustrated in FIG. 1 a and takes the form of a cam 13. When the camshaft 1 is manufactured, this cam 13 also has to be drawn onto the camshaft tube 3 and positioned axially and/or radially in suitable manner in relation to other components of the camshaft 1, i.e., the wearing disk 9 and/or the gear wheel 5 and, for example, other unillustrated cams or shafts radially and axially in suitable manner. It is also possible for this cam 13 and other components of the camshaft 1, which are not illustrated, to be secured to the camshaft tube 3 by being shrunk-fit. Moreover, a largely saucer-shaped delimiting element 17 that is arranged coaxially in relation to the collar 7 is secured to the gear wheel 5 by a securing device 15.

FIGS. 2 a and 2 b each schematically show portions of a second embodiment of a camshaft 19 according to the present invention, in which the camshaft 19 has a gear wheel seat. Individual components of this so-called assembled camshaft 19 are presented in a sectional illustration in FIG. 2 b. This camshaft 19 has a hollow, cylindrical camshaft tube 21 of constant wall thickness, a gear wheel 23 that is mounted directly onto an outer wall of the camshaft tube 21 at the end of the camshaft tube 21, for example by being shrunk-fit, and that has a lateral collar 27, and a locating bearing element that in this case is in the form of a cam 25 or special cam and is also mounted on the camshaft tube 21 by shrink-fitting.

A ring 29 is integrated in the cam 25. The gear wheel 23 having the attached collar 27 and the cam 25 are positioned radially and axially in relation to the camshaft tube 21 and in relation to one another. Thus, the lateral collar 27 of the gear wheel 23 and the ring 29 that is integrated in the cam 25 form or delimit, along an outer wall of the camshaft tube 21, a locating bearing seat 31 that is constructed for the purpose of receiving or providing a locating bearing or locating bearing ring (not illustrated).

Assembled camshafts 1, 19 as illustrated in FIGS. 1 a to 2 b are in principle made up of at least two components. The assembled camshafts 1, 19 that have been described above have the hollow-cylindrical camshaft tubes 3, 21, gear wheels 5, 23 mounted as end pieces on the camshaft tubes 3, 21 and having lateral collars 7, 27 and locating bearing elements such as the wearing disk 9 or the cam 25 having an integrated ring 29.

The camshafts 1, 19 from FIGS. 1 a to 2 b, in which the gear wheels 5, 23 having the collars 7, 27 are seated on cylindrical camshaft tubes 3, 21 that are also hollow in the region of the gear wheel seat, each have a smaller mass than the prior art camshaft 37 shown in FIGS. 3 a and 3 b, in which the gear wheel 35 is seated on a steel cylinder of solid material.

As a result of using the press-fit or welded flange 45, when the prior art camshaft 37 is manufactured an additional work step is produced. As a result, the prior art camshaft 37 is more complex to manufacture than the camshafts 1, 19 shown in FIGS. 1 a to 2 b. 

1.-10. (canceled)
 11. A camshaft, comprising a gear wheel mounted on a camshaft tube in a collar attached to the gear wheel and a locating bearing element mounted on the camshaft tube, with the gear wheel and the locating bearing element delimit a locating bearing seat.
 12. The camshaft as claimed in claim 11, wherein the gear wheel having the attached collar is shrunk-fit onto the camshaft tube.
 13. The camshaft as claimed in claim 11, wherein the locating bearing element comprises a wearing disk.
 14. The camshaft as claimed in claim 11, wherein the locating bearing element comprises a cam with an integrated ring.
 15. The camshaft as claimed in claim 14, wherein the gear wheel having the attached collar is shrunk-fit onto the camshaft tube.
 16. The camshaft as claimed in claim 11, wherein a locating seat is provided to axially secure the locating bearing element and the gear wheel having the attached collar.
 17. The camshaft as claimed in claim 11, wherein a length of the camshaft corresponds to a length of the camshaft tube and the gear wheel having the attached collar is mounted at an end of the camshaft tube.
 18. A method for manufacturing a camshaft in which a gear wheel is mounted on a camshaft tube, comprising attaching a collar to the gear wheel and mounting a locating bearing element on the camshaft tube such that the collar and locating bearing element provide a delimitation of a locating bearing seat for the camshaft.
 19. The method as claimed in claim 18, wherein characterized the gear wheel is shrunk-fit onto the camshaft tube.
 20. The method as claimed in claim 18, wherein the locating bearing element is shrunk-fit onto the camshaft tube.
 21. The method as claimed in claim 20, wherein characterized the gear wheel is shrunk-fit onto the camshaft tube.
 22. The method as claimed in claim 18, wherein the collar is attached to the gear wheel before mounting on the camshaft tube. 